1. Field of the Invention
The present invention relates to a color cathode ray tube, in particular, to that having anti-reflective and antistatic properties and capable of realizing high-contrast image display.
2. Description of the Related Art
Color cathode ray tubes to be used as color TV picture tubes or monitor tubes for information appliances and others have a vacuum vessel that comprises a panel, a neck for housing an electron gun therein, and a funnel for connecting the panel and the neck, in which the inner surface of the panel is coated with a phosphor layer in different colors to give a display screen, and plural (generally, three) electron beams as emitted by the electron gun housed in the neck are modulated according to image signals and impinge on the individual phosphors of different colors (generally, three colors) that constitute the phosphor layer to reproduce images.
FIG. 6 is a schematic sectional view showing an outline of the structure of a shadow mask-type color cathode ray tube, which is one example of color cathode ray tubes of that type. In FIG. 6, the reference numeral 1 indicates a panel, 2 indicates a neck, 3 indicates a funnel, 4 indicates a phosphor layer, 5 indicates a shadow mask, 6 indicates a mask frame, 7 indicates a shadow mask support mechanism, 8 indicates a support pin, 9 indicates a magnetic shield, 10 indicates an anode button, 11 indicates an internal electric conductive coating, 12 indicates a deflector, 13 indicates an electron gun, and 14 indicates three electron beams (red, green, blue).
In the color cathode ray tube of FIG. 6, the panel 1 to form a screen, the neck 2 for housing an electron gun therein, and the funnel 3 to connect the panel and the neck constitute a vacuum vessel. The inner surface of the vacuum vessel is coated with the internal electric conductive coating 11 via which the high cathode voltage as applied to the anode button 5 is transmitted to the inner surface of the screen and to the electron gun. The shadow mask 5 is welded to the mask frame 6, and is suspended between the support pins 8 that are embedded in the inner wall of the skirt portion of the panel 1, via the shadow mask support mechanism 7 therebetween. This is kept opposed to the phosphor layer 4 as formed on the inner surface of the panel 1, while being spaced from the phosphor layer 4 at a predetermined interval therebetween. The magnetic shield 9 is to shield the electron beams 14 from the external magnetic field of, for example, terrestrial magnetism, and this is kept welded to the mask frame 6.
The deflector 12 is mounted on the funnel in the position adjacent to the neck, by which are formed a horizontal magnetic field and a vertical magnetic field around the flow of the electron beams being emitted by the electron gun. In that condition, three electron beams as emitted by the electron gun 13 are deflected in two directions of a horizontal direction and a vertical direction, thereby to scan the phosphor layer 4 in the two-dimensional direction.
The cathode ray tube of that type is provided with an anti-reflective and antistatic film (film for surface treatment, hereinafter referred to as xe2x80x9csurface filmxe2x80x9d) which is for preventing the ambient light that enters the screen of the panel from reflecting to lower the contrast of the display image formed, and for preventing the panel from being electrostatically charged by the static electricity to be caused by the electron beam scanning.
FIG. 7 is to show one example of the anti-reflective structure for ambient light in the color cathode ray tube illustrated above. FIG. 7 is a schematic sectional view showing the portion A of FIG. 6 on an enlarged scale. In FIG. 7, the reference numeral 42 indicates a black matrix for partitioning the phosphor layer into plural color phosphors 43, thereby preventing color mixing so as to improve the contrast of the display image formed; 43 indicates three phosphors of red, green and blue; 44 indicates a metal back for generating a screen potential; 51 indicates an electron beam passing opening; R, G and B indicate electron beams of red, green and blue, respectively; 20 indicates an anti-reflective and antistatic film; 23 indicates the light emitted by the phosphor; 24 indicates ambient light; and 25 and 26 indicate reflected light from the ambient light 24. The other reference numerals that are the same as those in FIG. 6 correspond to those in FIG. 6.
As in FIG. 7, three electron beams R, G and B emitted by the electron gun are selected in color, while passing through the electron beam passing openings 51 of the shadow mask 5, and impinge on the individual phosphors 43. With the electron beams impinging thereon, the phosphors 43 are excited and emit light, and the emitted light runs outside through the panel 1 (toward the viewer looking at the display image). On the outer surface of the panel 1, formed is the anti-reflective and antistatic film 20. The anti-reflective and antistatic film 20 is composed of two layers, of which the first layer 20a is of a thin electric conductive film with high refractivity (having a refractive index of about 2), and the second layer 20b is of a thin, irregular reflective film having a lower refractive index (1.47) than the layer 20a. 
Of the ambient light 24 to enter the panel 1, the light 25 having penetrated into the anti-reflective and antistatic film 20 is absorbed by or interfered with the film 20, whereby its energy is attenuated, resulting in that the intensity of harmful reflected light that may degrade the display image formed could be lowered. In addition, the ambient light 24 reflects irregularly on the outer surface of the panel to give irregularly-reflected light 26, whereby the harmful reflection that may degrade the display image is retarded. The first layer 20a of an electric conductive film is connected with the earth outside the effective display region. The static electricity generated on the outer surface of the panel 1 flows to the earth via the first layer 20a, whereby the screen is prevented from being electrostatically charged.
In general, the anti-reflective and antistatic film 20 of that type is formed on the outer surface of the panel according to a so-called sol-gel method.
Concretely, the film 20 may be formed according to any of the following methods:
(1) A mixture composition capable of forming a layer with high refractivity, which is prepared by dispersing fine grains (having a grain size of at most tens nm) of an electric conductive oxide (e.g., ATO (antimony-doped tin oxide) or ITO (tin-doped indium oxide)) in an alcoholic solution, is applied onto glass for the panel 1 through so-called spin-coating to form a lower layer of an even film having a uniform thickness of from about 60 to about 100 nm, and a hydrolytic solution of a silicon alkoxide compound is applied thereover through spin-coating or spray-coating to form an upper layer of an even film having a uniform thickness of from about 80 nm to about 130 nm, thereby completing the formation of a two-layered, anti-reflective and antistatic film of those lower and upper layers on the glass.
(2) An antimony-doped, organic or inorganic tin compound is applied onto glass for the panel 1 through CVD (chemical vapor deposition) or LVD (liquid vapor deposition) to form an ATO film on the glass, and thereafter a hydrolytic solution of a silicon alkoxide compound is uniformly applied thereover to form a two-layered film having a uniform thickness of from about 80 nm to about 100 nm. In addition, for the purpose of reducing the reflected color density of the two-layered, anti-reflective and antistatic film and for reducing the reflectance thereof for visible rays falling within a wavelength range of from 380 nm to 780 nm, a hydrolytic solution of a silicon alkoxide compound is further sprayed over the two-layered film to form a third layer of a light-scattering film having a thickness of from about 10 nm to about 50 nm, and the surface of the third layer is roughened.
For example, Japanese Patent Laid-Open 4-334853 and Japanese Patent Laid-Open 5-343008 disclose the related arts as above.
Apart from the related arts (1) and (2), known is another related art to be mentioned below.
This is directed to a color cathode ray tube with antistatic and anti-reflective properties of increasing the contrast of images formed while preventing the brightness of the phosphors therein from lowering. For this, a first layer of a film having selective light absorbant and antistatic capabilities is formed on the outer surface of the panel by applying a coating liquid that contains a coloring material of, for example, dye, pigment and the like onto the outer surface of the panel, and thereafter another coating liquid containing an alkyl silicate compound in a solid phase is applied over the first layer to form thereon a second layer. In this related art, the first layer formed acts for selective light absorption and for prevention of static electrification, and the difference in the refractivity between the first layer and the second layer brings about the anti-reflective effect.
For the details of the related art of this type, for example, referred to are the disclosures of Japanese Patent Laid-Open 4-17242, Japanese Patent Laid-Open 4-137342, Japanese Patent Laid-Open 5-203804.
In addition to the above, further known is a method of coloring a panel with no anti-reflective and anti-static film formed on its outer surface, in which, however, the panel could not exhibit an anti-reflective and antistatic effect.
For the panel having selective light absorbability and coated, on its outer surface, with a surface film having anti-reflective and antistatic capabilities, the surface film shall be formed in a coating method for forming a thin film on the surface of glass for the panel. In this method, if the selective light absorbability of the panel is increased, the brightness of the phosphor screen is lowered and the phosphor screen is unfavorably colored, thereby resulting in that the screen shall have a chromatic body color to degrade the quality of the color display image formed. For these reasons, the method is problematic.
On the other hand, the technique of adding a coloring material such as pigment or dye to the transparent electric conductive layer (first layer, or lower layer) for the multi-layered film is also problematic in that the electroconductivity of the film is thereby lowered to degrade the antistatic capabilities of the film. Another problem in this is that the refractive index of the first layer is varied to degrade the anti-reflective capabilities of the film.
An object of the invention is to solve the problems with the related arts noted above, and to provide a color cathode ray tube having good anti-reflective and antistatic properties and capable of realizing high-quality image display.
In the color cathode ray tube of the invention that attains the object, the selective light absorbing capabilities of the screen are realized by a specific constituent material for panel glass and by a specific, multi-layered, surface film formed on the panel glass through coating. In the color cathode ray tube of the invention, the glass material for the panel contains a selective light absorbant additive of, for example, neodymium, neodymium oxide, erbium, erbium oxide and the like, in an amount of about 0.005% to about 1% by weight. Ions of neodymium, neodymium oxide, erbium, erbium oxide and others to be in the glass for the panel of the color cathode ray tube of the invention have selective light absorbing capabilities. Therefore, in the invention, the amount of the light absorbant material to be in the surface film on the outer surface of the panel glass is reduced. With that constitution, the body color of the screen of the color cathode ray tube of the invention is attenuated, and the antistatic property of the tube is prevented from being degraded. As a result, the color cathode ray tube of the invention has good anti-reflective and antistatic capabilities to give high-contrast display images.
Specifically, (1) the color cathode ray tube of the invention has a vacuum vessel comprising a panel, a neck for housing an electron gun therein, and a funnel for connecting the panel and the neck, in which the inner surface of the panel is coated with a phosphor layer in different colors to give a display screen, and the panel glass contains ions with selective light absorbability for visible rays (covering a wavelength range of from 380 nm to 780 nm) and is coated, on its outer surface, with a selective light absorbent surface film having low sheet resistivity and low reflectance.
The terminology, selective light absorption, as referred to herein for the panel glass or the surface film is meant to indicate that the spectral absorption pattern of the panel glass or the surface film gives an absorption maximum that can be differentiated from the base line in at least one or more specific wavelength ranges. This means that the white light having entered the panel glass or the surface film is selectively absorbed by the glass or the film, and runs out of it as chromatic transmitted light.
(2) For the color cathode ray tube of the invention, the panel glass as characterized by (1) contains any one or both of neodymium oxide and erbium oxide to have selective light absorbability in the visible ray region noted above.
(3) In the color cathode ray tube of the invention, the surface film as characterized by (1) is an anti-reflective and antistatic film having at least one layer.
(4) In the color cathode ray tube of the invention, the anti-reflective and antistatic film as characterized by (3) has a layer containing a dye.
(5) For the color cathode ray tube of the invention, light to be transmitted by the panel glass as characterized by (2) gives x of from 0.280 to 0.290 and y of from 0.285 to 0.305 in the CIE chromaticity diagram.
The substance to be added to the panel glass so as to make the panel glass have selective light absorbability for visible rays is not limited to neodymium oxide or erbium oxide mentioned above, but includes any other substances and ions having the ability of selective light absorption that is comparable to that of those oxides. Such other substances and ions include, for example, rare earth elements such as samarium, europium, praseodymium; rare earth ions such as samarium ion, europium ion, praseodymium ion; oxides of rare earth elements such as samarium, europium, praseodymium; ions of the oxides.
As mentioned hereinabove, the invention provides a high-quality color cathode ray tube which has selective light absorbing capabilities owing to the specific panel glass as combined with the specific surface film formed on the panel glass, and therefore realizes high-contrast image display. Owing to that combination, in addition, the color cathode ray tube of the invention has good antistatic capabilities and good anti-reflecting capabilities with the body color of the panel screen being attenuated.